Drivetrain 91' Mustang AOD Issues

5.0specialist

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Hello everyone. I have a 91' mustang gt convertible with some bolt-ons, 3.73 gears and a Broader Performance stage 1 valve body. Currently, I have the TV cable overly-adjusted to where it only allows the throttle body to open up 90 percent of the way during wide open throttle. This is the only way it will shift properly during normal driving without the shifts becoming too soft and having a hard time down shifting from 3rd automatically at low speeds (I have to literally floor it for it to down shift after a turn). The transmission came from another early 90's mustang and the stock valvebody that came with it had quite a bit of greyish residue/fluid. I had to change the filter twice already after the transmission swap due to the transmission dumping grey crud into the pan (cleaning itself out). It seems the previous owner never serviced it. So far, the transmission goes threw all of the gears with no abnormal slippage, but when slowing down in the OverDrive position, I have to help it by downshifting into Drive so it doesn't bog down the car when coming to a full stop. Other symptoms are shifting at 4100 rpms at full throttle in the Drive position and as I've mentioned, the cable needs to be overly tightened for it not to be so slushy and unresponsive during normal part-throttle operation. It currently has a brand new motorcraft trans filter in it and I've been using Valvoline Dex/Merc fluid with lubegard red bottle. I have also bought a new unused factory Ford AOD hi-rev governor (the 4900 rpm one), but I have not installed it yet. I'm wondering, if there is a possibility the current governor in the transmission might have a clogged screen filter (grey gunk) that can be reducing the TV pressure or maybe something else. Thank you for your help.
 
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John Dirks Jr

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If your TV cable prevents full throttle opening than obviously you have it adjusted wrong (even if intentionally). The problem here is when the throttle is in the resting (idle) position, the TV valve in the valve body would still be depressed and causing a higher line pressure that shouldn't be present with the throttle body in the closed position.

I recommend adjusting the TV cable properly first and then try to solve other problems. Setting the TV cable to a setting outside of the normal position is not going to solve a problem caused by something else. There is a very small amount of give or take from the recommended adjustment. Too far one way or the other will not be good.

Whats the history of the trans with regard to rebuilds or upgrades? These things are notorious for reverse band (controls OD) and intermediate sprag failure. Upgrading from 1.5 to 2" band and mechanical sprag is a common upgrade. Crud building up inside of the valve body and pan is a sign of internal component wear and failure. If things are excessively worn, you're chasing your tail doing anything short of a complete rebuild including the typical upgrades.
 

5.0specialist

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Jul 10, 2016
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pembroke pines, fl
If your TV cable prevents full throttle opening than obviously you have it adjusted wrong (even if intentionally). The problem here is when the throttle is in the resting (idle) position, the TV valve in the valve body would still be depressed and causing a higher line pressure that shouldn't be present with the throttle body in the closed position.

I recommend adjusting the TV cable properly first and then try to solve other problems. Setting the TV cable to a setting outside of the normal position is not going to solve a problem caused by something else. There is a very small amount of give or take from the recommended adjustment. Too far one way or the other will not be good.

Whats the history of the trans with regard to rebuilds or upgrades? These things are notorious for reverse band (controls OD) and intermediate sprag failure. Upgrading from 1.5 to 2" band and mechanical sprag is a common upgrade. Crud building up inside of the valve body and pan is a sign of internal component wear and failure. If things are excessively worn, you're chasing your tail doing anything short of a complete rebuild including the typical upgrades.
I don't know the history of the transmission. I bought it used from another mustang (92' or 93'). A few years back, I had discovered that my car had an aod from another pre-1989 ford vehicle that was not a mustang. That one was making weird noises, which led me to buying this current transmission that was for sale on craigslist. Currently, it has a Broader Performance stage 1 valvebody and a PA performance TV cable. Weird thing though, my previous transmission began showing the same exact symptoms (minus the weird noise) as this one when the valvebody I am using now was installed in that one. Can the valvebody be defective?
 

5.0specialist

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It seems this transmission just had a good amount of gunk in it to begin with and sat in a warehouse for awhile before being used again. I have corrected the fluid level since it was at the o of "Don't" on the factory dipstick above the cross hatches (too much fluid) and I have re adjusted the TV cable back to the normal "max" mark. Basically, I floored the accelerator pedal and my father pulled out the cable until it stopped and he tightened it to leave the cable in that position. It has zero slack and it allows the throttle to open up all the way. It seems the issue I've had before at this current cable adjustment has gotten much better due to the usage of good fluid and lubegard red bottle additive over time. I guess the transmission has been cleaning itself out. All of the shifts feel smooth,solid and quick. The 2nd to 3rd gear shift arrives a tad earlier during light throttle application now, but other than that, no other issues. The trans fluid I have siphoned out looks good and does not smell burnt. Next week, I will be installing a transgo hirev governor since I've read that 3.73 and higher gears can cause AOD's to shift extra early in the rpm range.
 
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5.0specialist

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Welp. I just found the problem causing the early shifts. Someone changed the governor and installed the factory low rev non-HO 4200 rpm governor. lol That is where it would shift at at wide open throttle. I took that one off and installed the new factory HO aod hirev governor. I could tell the old governor was swapped in because the extension housing was easy to take off (did not need to hit with a mallet) and the governor filter looked brand new. Also, the governor screws looked like someone worn it down with a drill bit. I haven't given it wide open throttle yet, but I could tell that my part throttle shift points were slightly higher. During light throttle, the car used to shift 2nd to 3rd at 15 mph. Now, it shifts into 3rd just as it passes 20 mph like my old 93' gt aod during light throttle.
 
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John Dirks Jr

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Glad to hear you’re getting it sorted out. The AOD does not have a great reputation. Having success with one is good news.
 
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